Wireless IC device

ABSTRACT

A wireless IC device includes a wireless IC element, a power supply circuit substrate including a laminate of a plurality of base layers and a power supply circuit connected to the wireless IC element, and a radiating element connected to the power supply circuit. The power supply circuit includes a first coil element connected in series with the wireless IC element, and a second coil element connected in parallel with the wireless IC element. The first coil element and the second coil element are wound and arranged such that winding axes of the first and second coil elements coincide or substantially coincide with each other and directions of magnetic fields generated in the respective first and second coil elements are opposite to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless IC device, and particularlyrelates to a wireless IC device preferably for use in an RFID (RadioFrequency Identification) system.

2. Description of the Related Art

In recent years, an RFID system has been put into practical use as anarticle information management system, which includes: a reader/writerthat generates an induction field; and an RFID tag (also referred to asa wireless IC device) that is attached to an article, and non-contactcommunication using the induction field is established between thereader/writer and the RFID tag to transmit predetermined informationtherebetween. The RFID tag is composed of a wireless IC chip that hasstored predetermined information therein and processes a predeterminedwireless signal; and an antenna that performs transmission/reception ofhigh-frequency signals. The RFID tag is attached to various articles asmanagement objects (or their packing materials) when used.

As RFID systems, a HF-band RFID system using the 13 MHz band and aUHF-band RFID system using the 900 MHz band are typically known.Particularly, with the UHF-band RFID system, the communication distanceis relatively long (the communication area is relatively wide), and itis possible to collectively perform reading/writing of a plurality oftags. Thus, the UHF-band RFID system is regarded as a promising systemfor article management.

As wireless IC devices for use in the UHF-band RFID system, for example,Japanese Patent Nos. 4069958 and 4561932 describe wireless IC devices inwhich a power supply circuit substrate is interposed between a wirelessIC element (wireless IC chip) and an antenna element. In these wirelessIC devices, the frequencies of transmission/reception signals arepractically determined by a power supply circuit provided on the powersupply circuit substrate. Thus, it is possible to easily realize stablehigh-frequency characteristics without being greatly influenced by thesize of the antenna element (radiating plate) and the surface area ofits periphery.

However, in each wireless IC device described above, when it isattempted to expand its frequency band, the power supply circuit becomescomplicated, some coil elements and capacitor elements have to beincorporated thereinto, and the necessity to ensure isolation betweenthese elements occurs. Thus, there is a problem that the size of thepower supply circuit substrate is increased.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a wireless ICdevice that allows a wide frequency band to be realized with asmall-size power supply circuit substrate.

A wireless IC device according to an aspect of a preferred embodiment ofthe present invention includes a wireless IC element, a power supplycircuit substrate including a laminate defined by laminated base layers,the power supply circuit substrate including a power supply circuitconnected to the wireless IC element, and a radiating element connectedto the power supply circuit. The power supply circuit includes a firstcoil element connected in series with the wireless IC element, and asecond coil element connected in parallel with the wireless IC element.The first coil element and the second coil element are wound andarranged such that winding axes of the first and second coil elementscoincide or substantially coincide with each other and directions ofmagnetic fields generated in the respective first and second coilelements are opposite to each other.

In the wireless IC device, since the first coil element and the secondcoil element are wound and arranged such that the winding axes of thefirst and second coil elements coincide or substantially coincide witheach other and the directions of the magnetic fields generated in therespective first and second coil elements are opposite to each other,coupling between each coil element is excellent, a plurality ofresonance points occurs, and transmission/reception of high-frequencysignals is possible in a wide frequency band. In addition, since thenumber of elements is small, the size of the power supply circuitsubstrate is reduced, and the size of the wireless IC device itself isalso reduced.

According to various preferred embodiments of the present invention, itis possible to realize a wide frequency band with a small-size powersupply circuit substrate.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a wireless IC device according to afirst preferred embodiment of the present invention.

FIG. 1B is a plan view of the wireless IC device of FIG. 1A.

FIG. 1C is a plan view of the wireless IC device in a state where apower-supply module is removed.

FIG. 2 is a schematic diagram showing the internal configuration of apower supply circuit substrate constituting the wireless IC device.

FIG. 3 is an equivalent circuit diagram of the wireless IC device.

FIG. 4 is a plan view showing a lamination structure of the power supplycircuit substrate in an exploded manner.

FIG. 5 is a graph showing a communication distance of the wireless ICdevice with respect to frequency.

FIG. 6A is a plan view of a wireless IC device according to a secondpreferred embodiment of the present invention.

FIG. 6B is a plan view of the wireless IC device in a state where apower-supply module is removed.

FIG. 7 is a Smith chart showing impedance characteristics of thewireless IC device according to the second preferred embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a wireless IC device according tothe present invention will be described with reference to theaccompanying drawings. It should be noted that in each drawing, commonelements and portions are denoted by the same reference numerals, andthe overlap description is omitted.

First Preferred Embodiment

A wireless IC device 1A according to a first preferred embodiment thatis preferably used for communication in the UHF band. As shown in FIGS.1A to 1C, the wireless IC device 1A includes a base sheet 10 havingflexibility and a rectangular or substantially rectangular shape, aradiating element 20 preferably including two radiating portions 21A and21B and connection portions 22A and 22B thereof, provided on a surfaceof the base sheet 10, and a power-supply module 30 connected to theradiating element 20, and is configured as a so-called RFID tag.

The base sheet 10 preferably has, for example, heat resistance orchemical resistance, and a thermoplastic resin material such aspolyimide or PET may be used for the base sheet 10. The radiatingelement 20 preferably has flexibility as a metal film which is providedsubstantially on the entirety of the surface of the base sheet 10 andcontains silver, copper, aluminum, or the like as a principal component.The radiating element 20 is divided into the two radiating portions 21Aand 21B across a gap at a center portion thereof in a longitudinaldirection, and the respective connection portions 22A and 22B areprovided so as to face the gap across which the radiating portions 21Aand 21B face each other. The power-supply module 30 is joined to theconnection portions 22A and 22B preferably by a conductive joiningmaterial 39 such as solder so as to extend over the gap. In other words,the radiating element 20 serves as a dipole type radiating element. Itshould be noted that the radiating element 20 except for the connectionportions 22A and 22B may be coated with a resist layer (e.g., apolyimide resin) which is not shown.

The power-supply module 30 includes a power supply circuit substrate 31and a wireless IC element (wireless IC chip 50). The wireless IC chip 50preferably includes a memory circuit, a clock circuit, a logic circuit,etc. and is an integrated circuit element which processes an RF signal.As shown in FIG. 2, the wireless IC chip 50 includes differentialinput/output electrodes 51A and 51B. The wireless IC chip 50 preferablyincludes a base defined by, for example, a semiconductor substrate suchas silicon. It should be noted that the wireless IC element may be abare chip IC or a package IC, for example.

A later-described power supply circuit 33 is included in the powersupply circuit substrate 31, and is electrically and directly connected(DC-connected) to end portions of the radiating element 20, namely, theconnection portions 22A and 22B, which are power-supply portions, by theconductive joining material 39 such as solder, for example.Specifically, in the power-supply module 30, the wireless IC chip 50 ismounted on the power supply circuit substrate 31 and is sealed by aresin material 55.

The power supply circuit substrate 31 preferably includes a laminate 32including a plurality of base layers (see FIG. 4) laminated on eachother, and includes the power supply circuit 33 shown in FIGS. 2 and 3.The power supply circuit 33 includes a first coil element L1 connectedin series with the wireless IC chip 50; and a second coil element L2connected in parallel with the wireless IC chip 50. An end of the firstcoil element L1 is connected to an electrode 34A, and the electrode 34Ais connected to the input/output electrode 51A of the wireless IC chip50 via a conductive joining material 52 such as solder. Another end ofthe first coil element L1 is connected to an input/output electrode 35Avia a capacitor element C1, and the input/output electrode 35A isconnected to the connection portion 22A of the radiating portion 21A viathe conductive joining material 39.

An end of the second coil element L2 is connected to the other end ofthe first coil element L1 and the capacitor element C1. Another end ofthe second coil element L2 is connected to an electrode 34B, and theelectrode 34B is joined to the input/output electrode 51B of thewireless IC chip 50 via the conductive joining material 52. Furthermore,the other end of the second coil element L2 is connected to aninput/output electrode 35B via a capacitor element C2, and theinput/output electrode 35B is connected to the connection portion 22B ofthe radiating portion 21B via the conductive joining material 39. Inother words, the first coil element L1 is connected in series with adifferential signal line, and the second coil element L2 is providedbetween differential signal lines.

The first coil element L1 and the second coil element L2 are wound andarranged such that the winding axes of the respective coil elements L1and L2 coincide or substantially coincide with each other and thedirections of magnetic fields M1 and M2 generated in the respective coilelements L1 and L2 are opposite to each other. Specifically, the coilelements L1 and L2 are arranged within the laminate 32 such that thewinding axes thereof extend along the lamination direction of thelaminate 32. In other words, as shown in FIG. 2, the direction of themagnetic field M1 generated by a current a in the first coil element L1and the direction of the magnetic field M2 generated by a current b inthe second coil element L2 are opposed to each other. The first coilelement L1 and the second coil element L2 are magnetically coupled toeach other as indicated by a reference character M, and the capacitorelements C1 and C2 define a resonant circuit. The resonant circuit alsoserves as an impedance matching circuit for the wireless IC chip 50 andthe radiating element 20.

The first coil element L1 is a series inductance component on thewireless IC chip 50 side, and this inductance component mainly has afunction to shift an impedance in the direction of an imaginary numberaxis on an impedance chart. Meanwhile, the second coil element L2 is aseries inductance component on the radiating element 20 side, isarranged so as to extend over the two connection portions 22A and 22B ofthe radiating element 20, and mainly has a function to shift animpedance on an imaginary number axis on an admittance chart. Asdescribed above, since the two types of the coil elements are caused tohave the respective functions as described above, it is possible toprovide efficient impedance matching.

Here, the lamination structure of the power supply circuit substrate 31(the laminate 32) will be described with reference to FIG. 4. Thelaminate 32 is preferably formed by laminating, pressure-bonding, andfiring base layers 41 a to 41 l formed from a dielectric material or amagnetic material. It should be noted that the base layers constitutingthe laminate 32 are not limited to a ceramic material, and may be, forexample, a thermosetting resin such as a liquid crystal polymer, or aresin such as a thermoplastic resin.

The base layers 41 a to 41 l are laminated such that the base layer 41 abecomes a lowermost layer and the base layer 41 l becomes an uppermostlayer. The input/output electrodes 35A and 35B are formed on a backsurface of the base layer 41 a, and via-hole conductors 61 a and 61 bare also formed therein. Capacitor electrodes 42A, 42B, 43A, 43B, 44A,and 44B are formed on front surfaces of the base layers 41 b, 41 c, and41 d, and via-hole conductors 62 a, 62 b, 63 a, and 63 b are also formedtherein. The via-hole conductors 63 a and 63 b are formed in the baselayer 41 e. Conductor lines 45A to 45F are formed on front surfaces ofthe base layers 41 f to 41 k, and the via-hole conductors 63 a to 63 hare also formed therein. The input/output electrodes 34A and 34B andmounting electrodes 34C and 34D are formed on a front surface of thebase layer 41 l, and the via-hole conductors 63 g and 63 h are alsoformed therein.

The power supply circuit 33 is preferably formed by laminating the baselayers 41 a to 41 l described above. In other words, the electrodes 35Aand 35B are connected to the capacitor electrodes 42A and 42B via thevia-hole conductors 61 a and 61 b, respectively. The capacitorelectrodes 42A and 42B are connected to the capacitor electrodes 44A and44B via the via-hole conductors 62 a and 62 b, respectively. Thecapacitor electrodes 44A and 44B are connected to an end and another endof the conductor line 45A via the via-hole conductors 63 a and 63 b,respectively. The capacitor electrodes 43A and 43B are connected to theend and the other end of the conductor line 45A via the via-holeconductors 63 a and 63 b, respectively.

The end of the conductor line 45A is connected to an end of theconductor line 45B via the via-hole conductor 63 a, and another end ofthe conductor line 45B is connected to an end of the conductor line 45Cvia the via-hole conductor 63 d. The other end of the conductor line 45Ais connected to an end of the conductor line 45F via the via-holeconductor 63 c, and another end of the conductor line 45F is connectedto the input/output electrode 34B via the via-hole conductor 63 h. Theconductor lines 45C, 45D, and 45E are connected to each other via thevia-hole conductors 63 e and 63 f in a spiral manner. Another end of theconductor line 45E is connected to the input/output electrode 34A viathe via-hole conductor 63 g.

With the connection mode described above, the capacitor electrodes 42A,43A, and 44A constitute the capacitor element C1, and the capacitorelectrodes 42B, 43B, and 43C constitute the capacitor element C2. Inaddition, the conductor lines 45C, 45D, and 45E constitute the firstcoil element L1, and the conductor line 45A constitutes the second coilelement L2.

In the wireless IC device 1A, when a predetermined high-frequency signalis transmitted from the wireless IC chip 50 via the power supply circuit33 to the radiating element 20, the high-frequency signal is radiatedfrom the radiating element 20 to the outside without any change. Also,when the radiating element 20 receives a high-frequency wave from theoutside, power is similarly supplied to the wireless IC chip 50 via thepower supply circuit 33. Thus, the wireless IC chip 50 and areader/writer, which is not shown, communicate with each other.

In the wireless IC device 1A, the first coil element L1 and the secondcoil element L2 are wound and arranged such that the winding axes of thecoil elements L1 and L2 coincide or substantially coincide with eachother and the directions of the magnetic fields M1 and M2 generated inthe respective coil elements L1 and L2 are opposite to each other. Thus,coupling between the coil elements L1 and L2 is excellent, a pluralityof resonance points occurs, and transmission/reception of high-frequencysignals is possible in a wide frequency band. In addition, since thenumber of elements is small, the size of the power supply circuitsubstrate 31 is reduced, and the size of the wireless IC device 1Aitself is also reduced.

With regard to the wireless IC device 1A using the power supply circuitsubstrate 31, its communication distance with respect to frequency isshown in FIG. 5. In FIG. 5, the communication distance is shown as aratio in which the longest distance is regarded as 1. The actualdistance depends on the gain of the radiating element 20. In addition, aregion in which impedance matching is provided between the radiatingelement 20 and the wireless IC chip 50 is made large, and two resonancepoints X and Y (see FIG. 5) occur.

In the power supply circuit 33, the first coil element L1 mainly servesas an inductance element for impedance matching, and the second coilelement L2 mainly serves as an inductance element constituting the powersupply circuit 33. The impedance of the imaginary part of the wirelessIC chip 50 is high in the negative direction, and the impedance of theimaginary part of the radiating element 20 is high in the positivedirection. Thus, the inductance value of the first coil element L1 ispreferably greater than the inductance value of the second coil elementL2. In addition, the ratio L1:L2 of the inductance values of the firstand second coil elements L1 and L2 is preferably about 3:1 to about 4:1,for example.

Second Preferred Embodiment

In a wireless IC device 1B according to a second preferred embodiment ofthe present invention, as shown in FIG. 6, the two radiating portions21A and 21B of the radiating element 20 preferably have a meander shape,and the other configuration is preferably the same or substantially thesame as that of the first preferred embodiment. The advantageous effectsof the wireless IC device 1B are the same as those of the firstpreferred embodiment.

The communication distance of the wireless IC device 1B with respect tofrequency shows substantially the same characteristics as in FIG. 5, andthe gain is increased since the radiating portions 21A and 21Bpreferably have a meander shape. Thus, the communication distance isslightly lengthened. In addition, impedance characteristics are shown inFIG. 7. In FIG. 7, an A part is a characteristic at 860 MHz, and a Bpart is a characteristic at 960 MHz. Since a C part is ring-shaped, aregion in which impedance matching is provided between the radiatingelement 20 and the wireless IC chip 50 is made large.

The impedance (imaginary part) of the wireless IC chip 50 preferably isabout −150Ω to about −250Ω, and the impedance (imaginary part) of theradiating element 20 preferably is about 50 to about 400Ω, for example.

It should be noted that the wireless IC device according to the presentinvention is not limited to the preferred embodiments described above,and can be variously modified within the scope of the present invention.

In particular, the materials, the shapes, and the sizes of the basesheet and the radiating element may be selected as appropriate accordingto the purpose. In addition, the shape of the radiating element isarbitrary, and may be a loop shape.

In addition, it is possible to use the wireless IC device not only as atag attached to an article but also as a reader/writer, and it is alsopossible to use the wireless IC device in a wireless communicationsystem other than an RFID system. Moreover, the wireless IC chip may bemounted on another substrate, other than being mounted on the powersupply circuit substrate.

Other than being provided exclusively, the radiating element may beconfigured using a ground conductor provided on a printed wiring board.In this case, the printed wiring board preferably is a body of thewireless IC device. In addition, the power supply circuit substrate maybe formed by a so-called semiconductor process as a rewiring layer ofthe wireless IC chip, for example.

As described above, preferred embodiments of the present invention areuseful for a wireless IC device, and are particularly excellent in thatit is possible to realize a wide frequency band with a small-size powersupply circuit substrate.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A wireless IC device comprising: a wireless ICelement; a power supply circuit substrate including a laminate of aplurality of base layers, and a power supply circuit connected to thewireless IC element; and a radiating element connected to the powersupply circuit; wherein the power supply circuit includes a first coilelement connected in series with the wireless IC element, and a secondcoil element connected in parallel with the wireless IC element; and thefirst coil element and the second coil element are wound and arrangedsuch that winding axes of the first and second coil elements coincide orsubstantially coincide with each other and directions of magnetic fieldsgenerated in the respective first and second coil elements are oppositeto each other.
 2. The wireless IC device according to claim 1, whereinthe first coil element and the second coil element are arranged withinthe laminate such that the winding axis of each coil element extendsalong a lamination direction of the base layers.
 3. The wireless ICdevice according to claim 1, wherein the power supply circuit includes afirst capacitor element and a second capacitor element which areconnected between both end portions of the second coil element and theradiating element; and the second coil element and the first and secondcapacitor elements constitute a resonant circuit.
 4. The wireless ICdevice according to claim 1, wherein the radiating element includes tworadiating portions and connection portions.
 5. The wireless IC deviceaccording to claim 4, wherein the two radiating portions are arranged toface each other across a gap at a center portion thereof in alongitudinal direction, and the connection portions are arranged to facethe gap across which the radiating portions face each other.
 6. Thewireless IC device according to claim 1, wherein the radiating elementincludes a flexible metal film.
 7. The wireless IC device according toclaim 1, wherein the radiating element is a dipole radiating element. 8.The wireless IC device according to claim 1, further comprising a resinmaterial arranged to cover the wireless IC element mounted on the powersupply circuit substrate.
 9. The wireless IC device according to claim1, wherein the first coil element is a series inductance component on aside of the wireless IC device and the second coil element is a seriesinductance component on a side of the radiating element.
 10. Thewireless IC device according to claim 1, wherein a ratio of inductancevalues of the first and second coil elements is about 3:1 or about 4:1.11. The wireless IC device according to claim 1, wherein the tworadiating portions have a meander shape.
 12. A wireless communicationsystem comprising the wireless IC device according to claim
 1. 13. Areader/writer apparatus comprising the wireless IC device according toclaim
 1. 14. An RFID device comprising the wireless IC device accordingto claim 1.